Air-cooled fuel cell system

ABSTRACT

To provide an air-cooled fuel cell system configured to suppress thermal runaway. An air-cooled fuel cell system, wherein the reaction air supply flow path comprises a first valve in a region downstream of the reaction air supplier and upstream of the reaction air inlet of the fuel cell; wherein the reaction air discharge flow path comprises a second valve downstream of the reaction air outlet of the fuel cell; wherein the fuel gas supply flow path comprises a third valve upstream of the fuel gas inlet of the fuel cell; wherein the fuel off-gas discharge flow path comprises a fourth valve downstream of the fuel gas outlet of the fuel cell.

TECHNICAL FIELD

The disclosure relates to an air-cooled fuel cell system.

BACKGROUND

A fuel cell (FC) is a power generation device which is composed of asingle unit fuel cell (hereinafter, it may be referred to as “cell”) ora fuel cell stack composed of stacked unit fuel cells (hereinafter, itmay be referred to as “stack”) and which generates electrical energy byelectrochemical reaction between fuel gas (e.g., hydrogen) and oxidantgas (e.g., oxygen). In many cases, the fuel gas and oxidant gas actuallysupplied to the fuel cell, are mixtures with gases that do notcontribute to oxidation and reduction. Especially, the oxidant gas isoften air containing oxygen.

Hereinafter, fuel gas and oxidant gas may be collectively and simplyreferred to as “reaction gas” or “gas”. Also, a single unit fuel celland a fuel cell stack composed of stacked unit cells may be referred toas “fuel cell”.

Various techniques relating to fuel cells mounted and used in fuel cellelectric vehicles (hereinafter may be referred to as “vehicle”) wereproposed.

For Example, Patent Literature 1 discloses a fuel cell system having astructure which enables the exhaust of unreacted air as an uncondensedvapor by mixing an air warmed by cooling a stack with the unreacted airexhausted through the stack to improve the efficiency and performance ofthe system with the size of total system miniaturized.

Patent Literature 2 discloses an air-cooled fuel cell.

Patent Literature 3 discloses a fuel cell cooling method.

Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No.2005-216852

Patent Literature 2: JP-A No. 1988-294670

Patent Literature 3: JP-A No. 1992-286869

An air-cooled fuel cell takes in air from the outside through an airinlet, and it divides the air into reaction gas and cooling gas for use.

Conventional air-cooled fuel cells including Patent Literature 1 cannotindependently control reaction air and cooling air and may cause adecrease in performance to overdrying or excessive humidification. Amethod for independently control reaction gas and cooling gas, such as ageneral water-cooled fuel cell system, is considered as an option tosolve the problem with air-cooled fuel cells. However, due to small heatcapacity of air which is used as the refrigerant in air-cooled fuelcells, if the water-cooled fuel cell system is applied to an air-cooledfuel cell system with no consideration for heat capacity, thermalrunaway is likely to occur compared to the case of using water as therefrigerant. Accordingly, there is a demand for a control method in thecase of using air having small heat capacity as the refrigerant.

SUMMARY

The present disclosure was achieved in light of the above circumstances.An object of the present disclosure is to provide an air-cooled fuelcell system configured to suppress thermal runaway.

The air-cooled fuel cell system of the present disclosure is anair-cooled fuel cell system,

wherein the air-cooled fuel cell system comprises:

a fuel cell,

an air introducer configured to take in air from the outside of theair-cooled fuel cell system,

a reaction air supplier configured to supply reaction air to the fuelcell,

a reaction air supply flow path configured to connect the reaction airsupplier and a reaction air inlet of the fuel cell,

a reaction air discharge flow path configured to connect a reaction airoutlet of the fuel cell and the outside;

a cooling air supply flow path configured to connect the air introducerand a cooling air inlet of the fuel cell,

a fuel gas supplier configured to supply fuel gas to the fuel cell,

a fuel gas supply flow path configured to connect the fuel gas supplierand a fuel gas inlet of the fuel cell,

a fuel off-gas discharge flow path configured to connect a fuel gasoutlet of the fuel cell and the outside,

a temperature acquirer configured to measure a temperature of the fuelcell, and

a controller;

wherein the reaction air supply flow path comprises a first valve in aregion downstream of the reaction air supplier and upstream of thereaction air inlet of the fuel cell;

wherein the reaction air discharge flow path comprises a second valvedownstream of the reaction air outlet of the fuel cell;

wherein the fuel gas supply flow path comprises a third valve upstreamof the fuel gas inlet of the fuel cell;

wherein the fuel off-gas discharge flow path comprises a fourth valvedownstream of the fuel gas outlet of the fuel cell;

wherein the fuel cell has a structure that a reaction air manifold and acooling air manifold are independent of each other;

wherein the controller monitors the temperature measured by thetemperature acquirer; and

wherein, when the temperature measured by the temperature acquirerexceeds a predetermined temperature threshold or when a temperatureincrease rate exceeds a predetermined temperature increase ratethreshold, the controller decreases opening degrees of the first,second, third and fourth valves.

The air-cooled fuel cell system may further comprise a cooling airdischarge flow path configured to connect a cooling air outlet of thefuel cell and the outside, and the cooling air discharge flow path maycomprise an air pump or air fan.

The controller may close the first, second, third and fourth valves whenpower generation of the fuel cell is stopped.

According to the air-cooled fuel cell system of the present disclosure,thermal runaway is suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a schematic configuration diagram of an example of theair-cooled fuel cell system of the present disclosure;

FIG. 2 is a schematic configuration diagram of another example of theair-cooled fuel cell system of the present disclosure; and

FIG. 3 is a flowchart of an example of the control of the air-cooledfuel cell system of the present disclosure.

DETAILED DESCRIPTION

The air-cooled fuel cell system of the present disclosure is anair-cooled fuel cell system,

wherein the air-cooled fuel cell system comprises:

a fuel cell,

an air introducer configured to take in air from the outside of theair-cooled fuel cell system,

a reaction air supplier configured to supply reaction air to the fuelcell,

a reaction air supply flow path configured to connect the reaction airsupplier and a reaction air inlet of the fuel cell,

a reaction air discharge flow path configured to connect a reaction airoutlet of the fuel cell and the outside,

a cooling air supply flow path configured to connect the air introducerand a cooling air inlet of the fuel cell,

a fuel gas supplier configured to supply fuel gas to the fuel cell,

a fuel gas supply flow path configured to connect the fuel gas supplierand a fuel gas inlet of the fuel cell,

a fuel off-gas discharge flow path configured to connect a fuel gasoutlet of the fuel cell and the outside,

a temperature acquirer configured to measure a temperature of the fuelcell, and

a controller;

wherein the reaction air supply flow path comprises a first valve in aregion downstream of the reaction air supplier and upstream of thereaction air inlet of the fuel cell;

wherein the reaction air discharge flow path comprises a second valvedownstream of the reaction air outlet of the fuel cell;

wherein the fuel gas supply flow path comprises a third valve upstreamof the fuel gas inlet of the fuel cell;

wherein the fuel off-gas discharge flow path comprises a fourth valvedownstream of the fuel gas outlet of the fuel cell;

wherein the fuel cell has a structure that a reaction air manifold and acooling air manifold are independent of each other;

wherein the controller monitors the temperature measured by thetemperature acquirer; and

wherein, when the temperature measured by the temperature acquirerexceeds a predetermined temperature threshold or when a temperatureincrease rate exceeds a predetermined temperature increase ratethreshold, the controller decreases opening degrees of the first,second, third and fourth valves.

According to the present disclosure, in the air-cooled fuel cell systemin which reaction air and cooling air are independently controlled, whenthe temperature of the fuel cell exceeds the predetermined temperaturethreshold or when the temperature increase rate exceeds thepredetermined rate threshold, the fuel cell system performs a controlsuch that the cooling air is not shut off while the reaction air is shutoff.

By the control, even if overheating occurs in the air-cooled fuel cellsystem in which air, which has smaller heat capacity than water, is usedas the refrigerant, the reaction air is put into an oxygen-deficientstate with cooling the fuel cell. Accordingly, thermal runaway issuppressed or prevented.

When the operation of the fuel cell is stopped, if the reaction airsystem (the oxidant gas system) is not sealed or if the amount ofresidual oxygen is larger than the amount of residual hydrogen in thesealed reaction air system, the oxygen is not be completely consumed bya reaction with residual hydrogen in the hydrogen system, and unconsumedoxygen is left. Even if the amount of the unconsumed oxygen is small, itmay lead to the progression of the degradation of the fuel cell. In theair-cooled fuel cell system, the fuel cell is more likely to degradesince the air flow path volume is larger than a water-cooled fuel cellsystem.

According to the present disclosure, the valves are disposed at the fuelcell inlet and outlet of the reaction air system to hermetically sealthe reaction air system. Accordingly, the flow of oxygen into thereaction air system is prevented; contamination of the reaction airsystem is prevented; and the degradation of the fuel cell is preventedwhen the power generation of the fuel cell is stopped.

When the power generation of the fuel cell is stopped, the amount ofhydrogen in moles of the sealed hydrogen system is increased more thantwice the amount of oxygen in moles of the sealed reaction air system.Accordingly, the fuel cell is sealed in a hydrogen-rich state.

If there is no valve at the fuel cell inlet and outlet of the reactionair system and if oxygen gradually enters such a reaction air system,the voltage of the fuel cell is indefinitely kept high. By disposing avalve at the fuel cell inlet and outlet of the reaction air system, thevoltage relatively quickly drops when the operation of the fuel cell isstopped. Accordingly, the fuel cell system of the present disclosure isexcellent in safety.

By the configuration of the present disclosure, even if the start andstop of the fuel cell is repeated, the fuel cell is resistant todegradation, and the lifetime of the fuel cell is increased severaltimes longer.

When the pressure of the reaction air system is not larger than thepressure of the cooling system, there is a possibility of contaminationfrom the cooling system to the reaction air system. If the reaction airsystem and the cooling system share an air pump, the flow rate andpressure of the reaction air and those of the cooling air cannot beindependently controlled.

By an oxidant gas pressure control valve at the outlet of the reactionair system, the flow rate and pressure of the reaction air iscontrolled. Accordingly, a decrease in the fuel cell performance due tooverdrying or excessive humidification, is prevented.

According to the present disclosure, during the operation of the fuelcell, the pressure of the reaction air system is increased higher thanthe pressure of the cooling system. For that reason, in the reaction airsystem, the reaction air supplier such as the air compressor is disposedat the reaction air inlet of the fuel cell, and the second valve such asan oxidant gas pressure control valve is disposed at the reaction airoutlet of the fuel cell. In the cooling system, a pressure loss unit isdisposed on the cooling air inlet side of the fuel cell, and arefrigerant driver such as a cooling fan is disposed on the cooling airoutlet side of the fuel cell. Accordingly, the pressure of the coolingair is decreased to lower than atmospheric pressure.

According to the present disclosure, by independently controlling theflow rate and pressure of the reaction air and those of the cooling air,the flow rate of the cooling air is increased and that of the reactionair is decreased in a high-temperature environment, thereby achievingthe optimization of the cell temperature and the retention of thehumidity.

According to the present disclosure, by independently controlling theflow rate and pressure of the reaction air and those of the cooling air,the flow rate of the cooling air is decreased and the flow rate of thereaction air is increased in a low-temperature environment, therebyachieving the optimization of the cell temperature and the enhancementof water discharge properties. Even in the case of using a simplesealing material which cannot fully isolate the cooling system and thereaction air system from each other, as long as the pressure of thereaction air system is higher than the pressure of the cooling system,cooling air contamination from the cooling system to the reaction airsystem is prevented.

The fuel cell system of the present disclosure is the air-cooled fuelcell system.

The air-cooled fuel cell system uses air as the refrigerant. In thepresent disclosure, air used as the refrigerant may be referred to as“cooling air”. Also in the present disclosure, air used as the oxidantgas may be referred to as “reaction air”.

The air-cooled fuel cell system includes the fuel cell, the airintroducer, the reaction air supplier, the reaction air supply flowpath, the reaction air discharge flow path, the cooling air supply flowpath, the fuel gas supplier, the fuel gas supply flow path, the fueloff-gas discharge flow path, the temperature acquirer, the controllerand so on.

The fuel cell generally includes a unit fuel cell.

The fuel cell may be a fuel cell composed of a single unit fuel cell, orit may be a fuel cell stack composed of stacked unit fuel cells.

The number of the stacked unit fuel cells is not particularly limited.For example, 2 to several hundred unit fuel cells may be stacked; 20 to600 unit fuel cells may be stacked; or 40 to 200 unit fuel cells may bestacked.

At both stacking-direction ends of each unit fuel cell, the fuel cellstack may include an end plate, a collector plate, a pressure plate andthe like.

Each unit fuel cell may include a membrane electrode gas diffusion layerassembly (MEGA). Each unit fuel cell may include first and secondseparators sandwiching the membrane electrode gas diffusion layerassembly.

The membrane electrode gas diffusion layer assembly includes a first gasdiffusion layer, a first catalyst layer, an electrolyte membrane, asecond catalyst layer and a second gas diffusion layer in this order.

More specifically, the membrane electrode gas diffusion layer assemblyincludes an anode-side gas diffusion layer, an anode catalyst layer, anelectrolyte membrane, a cathode catalyst layer and a cathode-side gasdiffusion layer in this order.

One of the first and second catalyst layers is the cathode catalystlayer, and the other is the anode catalyst layer.

The cathode (oxidant electrode) includes the cathode catalyst layer andthe cathode-side gas diffusion layer.

The anode (fuel electrode) includes the anode catalyst layer and theanode-side gas diffusion layer.

The first catalyst layer and the second catalyst layer are collectivelyreferred to as “catalyst layer”. The cathode catalyst layer and theanode catalyst layer are collectively referred to as “catalyst layer”.

One of the first gas diffusion layer and the second gas diffusion layeris the cathode-side gas diffusion layer, and the other is the anode-sidegas diffusion layer.

The first gas diffusion layer is the cathode-side gas diffusion layerwhen the first catalyst layer is the cathode catalyst layer. The firstgas diffusion layer is the anode-side gas diffusion layer when the firstcatalyst layer is the anode catalyst layer.

The second gas diffusion layer is the cathode-side gas diffusion layerwhen the second catalyst layer is the cathode catalyst layer. The secondgas diffusion layer is the anode-side gas diffusion layer when thesecond catalyst layer is the anode catalyst layer.

The first gas diffusion layer and the second gas diffusion layer arecollectively referred to as “gas diffusion layer” or “diffusion layer”.The cathode-side gas diffusion layer and the anode-side gas diffusionlayer are collectively referred to as “gas diffusion layer” or“diffusion layer”.

The gas diffusion layer may be a gas-permeable electroconductive memberor the like.

As the electroconductive member, examples include, but are not limitedto, a porous carbon material such as carbon cloth and carbon paper, anda porous metal material such as metal mesh and foam metal.

The fuel cell may include a microporous layer (MPL) between the catalystlayer and the gas diffusion layer. The microporous layer may contain amixture of a water repellent resin such as PTFE and an electroconductivematerial such as carbon black.

The electrolyte membrane may be a solid polymer electrolyte membrane. Asthe solid polymer electrolyte membrane, examples include, but are notlimited to, a hydrocarbon electrolyte membrane and a fluorineelectrolyte membrane such as a thin, moisture-containingperfluorosulfonic acid membrane. The electrolyte membrane may be aNafion membrane (manufactured by DuPont Co., Ltd.), for example.

One of the first separator and the second separator is the cathode-sideseparator, and the other is the anode-side separator.

The first separator is the cathode-side separator when the firstcatalyst layer is the cathode catalyst layer. The first separator is theanode-side separator when the first catalyst layer is the anode catalystlayer.

The second separator is the cathode-side separator when the secondcatalyst layer is the cathode catalyst layer. The second separator isthe anode-side separator when the second catalyst layer is the anodecatalyst layer.

The first separator and the second separator are collectively referredto as “separator”. The anode-side separator and the cathode-sideseparator are collectively referred to as “separator”.

The membrane electrode gas diffusion layer assembly is sandwiched by thefirst separator and the second separator.

The separator may include supply and discharge holes for allowing thefluid such as the reaction gas and the refrigerant to flow in thestacking direction of the unit fuel cells. When the refrigerant is gas,for example, cooling air may be used as the refrigerant.

As the supply hole, examples include, but are not limited to, a fuel gassupply hole, an oxidant gas supply hole, and a refrigerant supply hole.

As the discharge hole, examples include, but are not limited to, a fuelgas discharge hole, an oxidant gas discharge hole, and a refrigerantdischarge hole.

The separator may include one or more fuel gas supply holes, one or moreoxidant gas supply holes, one or more refrigerant supply holes asneeded, one or more fuel gas discharge holes, one or more oxidant gasdischarge holes, and one or more refrigerant discharge holes as needed.

The separator may include a reaction gas flow path on a surface incontact with the gas diffusion layer. Also, the separator may include arefrigerant flow path for keeping the fuel cell temperature constant, onthe surface opposite to the surface in contact with the gas diffusionlayer.

When the separator is the anode-side separator, it may include one ormore fuel gas supply holes, one or more oxidant gas supply holes, one ormore refrigerant supply holes as needed, one or more fuel gas dischargeholes, one or more oxidant gas discharge holes, and one or morerefrigerant discharge holes as needed. The anode-side separator mayinclude a fuel gas flow path for allowing the fuel gas to flow from thefuel gas supply hole to the fuel gas discharge hole, on the surface incontact with the anode-side gas diffusion layer. As needed, theanode-side separator may include a refrigerant flow path for allowingthe refrigerant to from the refrigerant supply hole to the refrigerantdischarge hole, on the surface opposite to the surface in contact withthe anode-side gas diffusion layer.

When the separator is the cathode-side separator, it may include one ormore fuel gas supply holes, one or more oxidant gas supply holes, one ormore refrigerant supply holes as needed, one or more fuel gas dischargeholes, one or more oxidant gas discharge holes, and one or morerefrigerant discharge holes as needed. The cathode-side separator mayinclude an oxidant gas flow path for allowing the oxidant gas to flowfrom the oxidant gas supply hole to the oxidant gas discharge hole, onthe surface in contact with the cathode-side gas diffusion layer. Asneeded, the cathode-side separator may include a refrigerant flow pathfor allowing the refrigerant to flow from the refrigerant supply hole tothe refrigerant discharge hole, on the surface opposite to the surfacein contact with the cathode-side gas diffusion layer.

The separator may be a gas-impermeable electroconductive member or thelike. As the electroconductive member, examples include, but are notlimited to, a resin material such as thermosetting resin, thermoplasticresin and resin fiber, a carbon composite material obtained bypress-molding a mixture containing a carbonaceous material such ascarbon powder and carbon fiber, gas-impermeable dense carbon obtained bycarbon densification, and a metal plate (such as a titanium plate, aniron plate, an aluminum plate and a stainless-steel (SUS) plate)obtained by press-molding. The separator may function as a collector.

The shape of the separator may be a rectangular shape, a horizontalhexagon shape, a horizontal octagon shape, a circular shape or a longcircular shape, for example.

The fuel cell may include a manifold such as an inlet manifoldcommunicating between the supply holes and an outlet manifoldcommunicating between the discharge holes.

As the inlet manifold, examples include, but are not limited to, ananode inlet manifold, a reaction air inlet manifold (a cathode inletmanifold) and a cooling air inlet manifold.

As the outlet manifold, examples include, but are not limited to, ananode outlet manifold, a reaction air outlet manifold (a cathode outletmanifold) and a cooling air outlet manifold.

In the present disclosure, the reaction air inlet manifold (the cathodeinlet manifold) and the reaction air outlet manifold (the cathode outletmanifold) are collectively referred to as “reaction air manifold”.

Also in the present disclosure, the cooling air inlet manifold and thecooling air outlet manifold are collectively referred to as “cooling airmanifold”.

The fuel cell has the structure that the reaction air manifold and thecooling air manifold are independent of each other.

In the present disclosure, the fuel gas and the oxidant gas arecollectively referred to as “reaction gas”. The reaction gas supplied tothe anode is the fuel gas, and the reaction gas supplied to the cathodeis the oxidant gas. The fuel gas is a gas mainly containing hydrogen,and it may be hydrogen. The oxidant gas may be oxygen, air, dry air orthe like.

The fuel cell may include a resin frame.

The resin frame may be disposed in the periphery of the membraneelectrode gas diffusion layer assembly and may be disposed between thefirst separator and the second separator.

The resin frame may be a component for preventing cross leakage or ashort circuit between the catalyst layers of the membrane electrode gasdiffusion layer assembly.

The resin frame may include a skeleton, an opening, supply holes anddischarge holes.

The skeleton is a main part of the resin frame, and it connects to themembrane electrode gas diffusion layer assembly.

The opening is a region retaining the membrane electrode gas diffusionlayer assembly, and it is also a through-hole penetrating a part of theskeleton to set the membrane electrode gas diffusion layer assemblytherein. In the resin frame, the opening may be disposed in the positionwhere the skeleton is disposed around (in the periphery) of the membraneelectrode gas diffusion layer assembly, or it may be disposed in thecenter of the resin frame.

The supply and discharge holes allows the reaction gas, the refrigerantand the like to flow in the stacking direction of the unit fuel cells.The supply holes of the resin frame may be aligned and disposed tocommunicate with the supply holes of the separator. The discharge holesof the resin frame may be aligned and disposed to communicate with thedischarge holes of the separator.

The resin frame may include a frame-shaped core layer and twoframe-shaped shell layers disposed on both surfaces of the core layer,that is, a first shell layer and a second shell layer.

Like the core layer, the first shell layer and the second shell layermay be disposed in a frame shape on both surfaces of the core layer.

The core layer may be a structural member which has gas sealingproperties and insulating properties. The core layer may be formed of amaterial such that the structure is unchanged at the temperature of hotpressing in a fuel cell production process. As the material for the corelayer, examples include, but are not limited to, resins such aspolyethylene, polypropylene, polycarbonate (PC), polyphenylene sulfide(PPS), polyethylene terephthalate (PET), polyethylene naphthalate (PEN),polyamide (PA), polyimide (PI), polystyrene (PS), polyphenylene ether(PPE), polyether ether ketone (PEEK), cycloolefin, polyethersulfone(PES), polyphenylsulfone (PPSU), liquid crystal polymer (LCP) and epoxyresin. The material for the core layer may be a rubber material such asethylene propylene diene rubber (EPDM), fluorine-based rubber andsilicon-based rubber.

From the viewpoint of ensuring insulating properties, the thickness ofthe core layer may be 5 μm or more, or it may be 30 μm or more. From theviewpoint of reducing the cell thickness, the thickness of the corelayer may be 200 μm or less, or it may be 150 μm or less.

To attach the core layer to the anode-side and cathode-side separatorsand to ensure sealing properties, the first shell layer and the secondshell layer may have the following properties: the first and secondshell layers have high adhesion to other substances; they are softenedat the temperature of hot pressing; and they have lower viscosity andlower melting point than the core layer. More specifically, the firstshell layer and the second shell layer may be thermoplastic resin suchas polyester-based resin and modified olefin-based resin, or they may bethermosetting resin such as modified epoxy resin. The first shell layerand the second shell layer may be the same kind of resin as the adhesivelayer.

The resin for forming the first shell layer and the resin for formingthe second shell layer may be the same kind of resin, or they may bedifferent kinds of resins. By disposing the shell layers on bothsurfaces of the core layer, it becomes easy to attach the resin frameand the two separators by hot pressing.

From the viewpoint of ensuring adhesion, the thickness of the first andsecond shell layers may be 5 μm or more, or it may be 20 μm or more.From the viewpoint of reducing the cell thickness, the thickness of thefirst and second shall layers may be 100 μm or less, or it may be 40 μmor less.

In the resin frame, the first shell layer may be disposed only at a partthat is attached to the anode-side separator, and the second shell layermay be disposed only at a part attached to the cathode-side separator.The first shell layer disposed on one surface of the core layer may beattached to the cathode-side separator. The second shell layer disposedon the other surface of the core layer may be attached to the anode-sideseparator. The resin frame may be sandwiched by the pair of separators.

The fuel cell may include a gasket between adjacent unit fuel cells.

The material for the gasket may be ethylene propylene diene monomer(EPDM) rubber, silicon rubber, thermoplastic elastomer resin or thelike.

The fuel cell may include a cooling fin made of a metal. As the metal,examples include, but are not limited to, Al, Ti and SUS. The fuel cellmay include the cooling fin between the adjacent unit fuel cells.

The cooling fin may be a corrugated plate including concave groovesconfigured to function as a refrigerant flow path.

As the cooling fin, for example, a corrugated metal plate obtained byfolding a metal plate may be used. The surface of the cooling fin may besubjected to conductive treatment with silver, nickel, carbon or thelike.

The concave grooves of the cooling fin may be formed by folding themetal plate.

The depth of the concave grooves may be from 1.0 mm to 2.0 mm, forexample.

The metal plate may be folded to form concave grooves with a depth offrom 1.0 mm to 2.0 mm at a pitch of from 1.0 mm to 2.0 mm, for example,thereby preparing the corrugated cooling fin.

As long as the cooling fin is disposed between the adjacent unit fuelcells, the cooling fin may be disposed in at least a part of the regionin the planar direction between the adjacent unit fuel cells.

The cooling fin may be disposed in a region which is between the unitfuel cells adjacent to each other in the planar direction and whichfaces at least the MEGA.

The cooling fin may be disposed in a region which is other than theregion where the gasket is disposed between the unit fuel cells adjacentto each other in the planar direction.

The cooling fin may include a protrusion protruding from the unit fuelcell.

The shape of the cooling fin may be a rectangular shape, a horizontalhexagon shape, a horizontal octagon shape, a circular shape or a longcircular shape, for example.

As the air system, the air-cooled fuel cell system includes the airintroducer.

The air introducer takes in air from the outside of the air-cooled fuelcell system.

The air introducer may be an air inlet, for example.

A pressure loss unit may be disposed in the air introducer. As thepressure loss unit, examples include, but are not limited to, a filter.

The air introducer may include an air divider. The air divider dividesthe air taken in from the outside into the reaction air and the coolingair before the air is introduced to the fuel cell. The air divider isnot always necessary when a reaction air introducer configured to takein the reaction air from the outside and a cooling air introducerconfigured to take in the cooling air from the outside, are disposed asthe air introducer.

The air divider may divide the air into the reaction air and the coolingair at a flow rate ratio of from 1:20 to 1:50.

For example, the air divider may be a housing capable of taking in air.The material for the housing is not particularly limited, and it may bea metal, a resin or a carbonaceous material, for example.

The fuel cell system includes the cooling system of the fuel cell.

The cooling system may include the cooling air supply flow path.

The cooling air supply flow path connects the air introducer and thecooling air inlet of the fuel cell. The cooling air inlet may be arefrigerant supply hole, a cooling air inlet manifold, or the like.

The cooling system may include the cooling air discharge flow path.

The cooling air discharge flow path connects the cooling air outlet ofthe fuel cell and the outside. The cooling air outlet may be arefrigerant discharge hole, a cooling air outlet manifold, or the like.

The cooling air discharge flow path may include a refrigerant driver.

The refrigerant driver is electrically connected to the controller. Therefrigerant driver is operated according to a control signal from thecontroller. The flow rate of the refrigerant supplied from therefrigerant driver to the fuel cell is controlled by the controller. Thetemperature of the fuel cell may be controlled thereby.

As the refrigerant driver, examples include, but are not limited to, anair pump, an air compressor, an air blower and an air fan.

In the cooling system, by disposing the refrigerant driver on thecooling air outlet side, the pressure inside the cooling air manifold ofthe fuel cell is controlled to atmospheric pressure or less.

The structure of the cooling system is an atmospheric release structurehaving no valve, and the pressure of the cooling air is equal to theoutside pressure (e.g., −0.01 kPaG to −0.3 kPaG). Accordingly, the fuelcell structure is prevented from being exposed to stress associated withpressure difference, and the use of a lightweight, inexpensive housingmaterial is allowed. More specifically, the cooling air supply flow pathand/or the cooling air discharge flow path may be a pipe.

The fuel cell system includes an oxidant gas system (a reaction airsystem).

The oxidant gas system may include the reaction air supplier, thereaction air supply flow path, the reaction air discharge flow path, areaction air bypass flow path, a bypass valve, a reaction air flow ratesensor and so on. More specifically, the reaction air supply flow path,the reaction air discharge flow path and/or the reaction air bypass flowpath may be a pipe.

The reaction air supplier supplies the reaction air to the fuel cell.More specifically, the reaction air supplier supplies the reaction airto the cathode of the fuel cell.

The sealed volume of the oxidant gas system may be 5 times or less thesealed volume of a fuel gas system.

As the reaction air supplier, examples include, but are not limited to,an air pump, an air compressor, an air blower and an air fan.

In the oxidant gas system, the reaction air supplier is independentlydisposed before the introduction of the reaction air into the fuel cell.By independently disposing the refrigerant driver and the reaction airsupplier in the cooling system and the oxidant gas system, respectively,the flow rate of the cooling air and that of the reaction air isindependently controlled; the water discharge properties and thehumidity is precisely controlled; and the power generation performanceof the fuel cell is increased.

The reaction air supplier is electrically connected to the controller.The reaction air supplier is operated according to a control signal fromthe controller. At least one selected from the group consisting of theflow rate and pressure of the reaction air supplied from the reactionair supplier to the cathode, may be controlled by the controller.

The reaction air supply flow path connects the reaction air supplier andthe reaction air inlet of the fuel cell. The reaction air supply flowpath allows the reaction air to be supplied from the reaction airsupplier to the cathode of the fuel cell. The reaction air inlet may bethe oxidant gas supply hole, the cathode inlet manifold, or the like.The reaction air supply flow path may branch from the air divider.

The reaction air supply flow path comprises the first valve in theregion downstream of the reaction air supplier and upstream of thereaction air inlet of the fuel cell.

The first valve may be directly disposed at the reaction air inlet ofthe fuel cell.

The first valve may be disposed upstream of the reaction air supplier.

The first valve is electrically controlled to the controller. By openingthe first valve by the controller, the reaction air is supplied from thereaction air supply flow path to the reaction air inlet of the fuelcell.

A pressure loss unit may be disposed upstream of the reaction airsupplier of the reaction air supply flow path. As the pressure lossunit, examples include, but are not limited to, a filter. As thepressure loss unit disposed in the reaction air supply flow path, forexample, a filter which is finer and higher in pressure loss than thepressure loss unit disposed in the air introducer, may be used. Bycleaning the whole of the air introduction system, the energy loss ofthe fuel cell is increased. However, by cleaning only the oxidant gassystem, the energy loss of the fuel cell is suppressed. By virtue of theuse of the finer filter, the contamination of the cooling air isreduced, and the durability of the fuel cell is increased.

The reaction air discharge flow path connects the reaction air outlet ofthe fuel cell and the outside of the air-cooled fuel cell system. Thereaction air discharge flow path allows the reaction air, which isdischarged from the cathode of the fuel cell, to be discharged to theoutside of the air-cooled fuel cell system. The reaction air outlet maybe the oxidant gas discharge hole, the cathode outlet manifold, or thelike.

The reaction air discharge flow path comprises the second valvedownstream of the reaction air outlet of the fuel cell. The second valvemay be a sealing valve or an oxidant gas pressure control valve.

The second valve is electrically connected to the controller. By openingthe second valve by the controller, the reaction air is discharged tothe outside from the reaction air discharge flow path. The pressure ofthe reaction air supplied to the cathode (cathode pressure) may becontrolled by controlling the opening degree of the second valve.

The reaction air bypass flow path branches from the reaction air supplyflow path, bypasses the fuel cell, and connects the branch of thereaction air supply flow path and the junction of the reaction airdischarge flow path.

The bypass valve is disposed in the reaction air bypass flow path.

The bypass valve is electrically connected to the controller. By openingthe bypass valve by the controller, when the supply of the reaction airto the fuel cell is unnecessary, the reaction air is allowed to bypassthe fuel cell and be discharged to the outside from the reaction airdischarge flow path. The first valve may be a three-way valve, so thatthe first valve also functions as a bypass valve.

The reaction air flow rate sensor may be disposed in the reaction airsupply flow path.

The reaction air flow rate sensor detects the flow rate of the reactionair in the oxidant gas system. The reaction air flow rate sensor iselectrically connected to the controller. The controller may estimatethe rotational speed of the air compressor from the flow rate of thereaction air detected by the reaction air flow rate sensor. The reactionair flow rate sensor may be disposed upstream from the reaction airsupplier of the reaction air supply flow path.

As the reaction air flow rate sensor, a conventionally-known flow meteror the like may be used.

For the oxidant gas system, by the inlet-side reaction air supplier andthe second valve, the pressure inside the reaction air manifold of thefuel cell can be a pressure that is equal to or more than atmosphericpressure (e.g., 5 kPaG to 15 kPaG).

The pressure of the reaction air is increased by the second valve of theoxidant gas system. Accordingly, the fuel cell performance is increasedby increased oxygen partial pressure and prevention of drying of thefuel cell.

When the oxidant gas system and the cooling system are not separated, itis also necessary to increase the pressure of the cooling air which isat a flow rate that is approximately 30 times the flow rate of thereaction air. As a result, the energy loss which is produced when theoxidant gas system and the cooling system are not separated, is 30 ormore times larger than the energy loss which is produced when theoxidant gas system and the cooling system are separated.

The fuel cell system includes a fuel gas system.

The fuel gas system supplies fuel gas to the fuel cell.

The fuel gas system includes a fuel gas supplier.

The fuel gas supplier supplies the fuel gas to the anode of the fuelcell.

As the fuel gas supplier, examples include, but are not limited to, afuel tank such as a liquid hydrogen tank and a compressed hydrogen tank.

The fuel gas supplier is electrically connected to the controller. Inthe fuel gas supplier, ON/OFF of the fuel gas supply to the fuel cellmay be controlled by controlling the opening and closing of the mainshutoff valve of the fuel gas supplier according to a control signalfrom the controller.

The fuel gas system includes the fuel gas supply flow path. Morespecifically, the fuel gas supply flow path may be a pipe.

The fuel gas supply flow path connects the fuel gas supplier and thefuel gas inlet of the fuel cell. The fuel gas supply flow path allowsthe fuel gas to be supplied to the anode of the fuel cell. The fuel gasinlet may be the fuel gas supply hole, the anode inlet manifold, or thelike.

The fuel gas supply flow path comprises the third valve upstream of thefuel gas inlet of the fuel cell.

The third valve may be directly disposed at the fuel gas inlet of thefuel cell.

The third valve may be disposed upstream of an ejector.

The third valve is electrically connected to the controller. By openingthe third valve by the controller, the fuel gas is supplied from thefuel gas supply flow path to the fuel gas inlet of the fuel cell.

In the fuel gas supply flow path, the ejector may be disposed.

For example, the ejector may be disposed at a junction with acirculation flow path on the fuel gas supply flow path. The ejectorsupplies a mixed gas containing fuel gas and circulation gas to theanode of the fuel cell. As the ejector, a conventionally-known ejectormay be used.

A pressure control valve and a medium-pressure hydrogen sensor may bedisposed in a region between the fuel gas supplier and ejector of thefuel gas supply flow path.

The pressure control valve controls the pressure of the fuel gassupplied from the fuel gas supplier to the ejector.

The pressure control valve is electrically connected to the controller.The pressure of the fuel gas supplied to the ejector may be controlledby controlling the opening/closing, opening degree or the like of thepressure control valve by the controller.

The medium-pressure hydrogen sensor is electrically connected to thecontroller. The controller detects the fuel gas pressure measured by themedium-pressure hydrogen sensor. The pressure of the fuel gas suppliedto the ejector may be controlled by controlling the opening/closing,opening degree or the like of the pressure control valve, based on thedetected pressure.

The fuel gas system includes the fuel off-gas discharge flow path. Morespecifically, the fuel off-gas discharge flow path may be a pipe.

The fuel off-gas discharge flow path connects the fuel gas outlet of thefuel cell and the outside of the fuel cell system.

In the fuel off-gas discharge flow path, a gas-liquid separator may bedisposed in a region between the fuel gas outlet and the outside of thefuel cell system.

The fuel off-gas discharge flow path may branch from the circulationflow path through the gas-liquid separator.

The fuel off-gas discharge flow path discharges, to the outside of thefuel cell system, the fuel off-gas discharged from the fuel gas outletof the fuel cell. The fuel gas outlet may be the fuel gas dischargehole, the anode outlet manifold, or the like.

The fuel off-gas discharge flow path comprises the fourth valve (a fueloff-gas discharge valve or a gas and water discharge valve) downstreamof the fuel gas outlet of the fuel cell.

The fourth valve may be directly disposed at the fuel gas outlet of thefuel cell.

The fourth valve may be disposed downstream from the gas-liquidseparator in the fuel off-gas discharge flow path.

The fourth valve allows the fuel off-gas, water and the like to bedischarged to the outside (of the system). The outside may be theoutside of the fuel cell system, or it may be the outside of thevehicle.

The fourth valve may be electrically connected to the controller, andthe flow rate of the fuel off-gas discharged to the outside and the flowrate of the discharged water (liquid water) may be controlled bycontrolling the opening and closing of the fourth valve by thecontroller. By controlling the opening degree of the fourth valve, thepressure of the fuel gas supplied to the anode of the fuel cell (anodepressure) may be controlled.

The fuel off-gas may contain the fuel gas that has passed through theanode without reacting, and the water generated at the cathode anddelivered to the anode. In some cases, the fuel off-gas containscorroded substances generated in the catalyst layer, the electrolytemembrane or the like, and the oxidant gas or the like allowed to besupplied to the anode during a purge.

The fuel gas system may include the circulation flow path. Morespecifically, the circulation flow path may be a pipe.

The circulation flow path may connect the fuel gas outlet of the fuelcell and the ejector.

The circulation flow path may branch from the fuel off-gas dischargeflow path and connect to the ejector disposed in the fuel gas supplyflow path, thereby merging with the fuel gas supply flow path.

The circulation flow path may branch from the fuel off-gas dischargeflow path through the gas-liquid separator and connect to the ejectordisposed in the fuel gas supply flow path, thereby merging with the fuelgas supply flow path.

The circulation flow path allows the fuel off-gas, which is the fuel gasdischarged from the fuel gas outlet of the fuel cell, to be recoveredand supplied to the fuel cell as the circulation gas.

A gas circulation pump may be disposed in the circulation flow path. Thegas circulation pump circulates the fuel off-gas as the circulation gas.The gas circulation pump may be electrically connected to thecontroller, and the flow rate of the circulation gas may be controlledby controlling ON/OFF, rotational speed, etc., of the gas circulationpump by the controller.

The gas-liquid separator (anode gas-liquid separator) may be disposed inthe circulation flow path.

The gas-liquid separator may be disposed at the branch point of the fueloff-gas discharge flow path and the circulation flow path. Accordingly,the flow path from the fuel gas outlet to the gas-liquid separator maybe the fuel off-gas discharge flow path or the circulation flow path.

The gas-liquid separator is disposed upstream from the fourth valve ofthe fuel off-gas discharge flow path.

The gas-liquid separator separates the water (liquid water) and the fueloff-gas which is the fuel gas discharged from the fuel gas outlet.Accordingly, the fuel off-gas may be returned to the circulation flowpath as the circulation gas, or unnecessary gas, water and the like maybe discharged to the outside by opening the gas and water dischargevalve of the fuel off-gas discharge flow path. In addition, by thegas-liquid separator, the flow of excess water into the circulation flowpath is suppressed. Accordingly, the occurrence of freezing of thecirculation pump or the like due to the water, is suppressed.

The temperature acquirer measures the temperature of the fuel cell.

The temperature acquirer is electrically connected to the controller.The controller detects the temperature of the fuel cell measured by thetemperature acquirer.

As the temperature acquirer, a conventionally-known temperature sensor,a thermometer or the like may be used.

The fuel cell system may include a secondary cell.

The secondary cell (battery) may be any chargeable and dischargeablebattery. For example, it may be a conventionally-known secondary cellsuch as a nickel-hydrogen secondary cell and a lithium ion secondarycell. The secondary cell may include a power storage element such as anelectric double layer capacitor. The secondary cell may have a structuresuch that a plurality of secondary cells are connected in series. Thesecondary cell supplies power to a motor, an air compressor and thelike. The secondary cell may be chargeable by a power source outside thevehicle. The secondary cell may be charged by the output power of thefuel cell. The charge and discharge of the secondary cell may becontrolled by the controller.

The controller physically includes a processing unit such as a centralprocessing unit (CPU), a memory device such as a read-only memory (ROM)and a random access memory (RAM), and an input-output interface. The ROMis used to store a control program, control data and so on to beprocessed by the CPU, and the RAM is mainly used as various workspacesfor control processing. The controller may be a control device such asan electronic control unit (ECU).

The controller may be electrically connected to an ignition switch whichmay be mounted in the vehicle. The controller may be operable by anexternal power source even if the ignition switch is turned OFF.

The controller monitors the temperature measured by the temperatureacquirer. During the operation of the fuel cell, the controller maymonitor the temperature measured by the temperature acquirer.

When the temperature measured by the temperature acquirer exceeds thepredetermined temperature threshold or when the temperature increaserate exceeds the predetermined temperature increase rate threshold, thecontroller decreases the opening degrees of the first, second, third andfourth valves.

When the temperature measured by the temperature acquirer exceeds thepredetermined temperature threshold or when the temperature increaserate exceeds the predetermined temperature increase rate threshold, thecontroller may stop the power generation of the fuel cell.

The controller may close the first, second, third and fourth valves whenthe power generation of the fuel cell is stopped.

The predetermined temperature threshold and the predetermined ratethreshold may be appropriately set depending on the performance of thefuel cell.

FIG. 1 is a schematic configuration diagram of an example of theair-cooled fuel cell system of the present disclosure.

The air-cooled fuel cell system shown in FIG. 1 includes a fuel cell 10,an air system 20, an oxidant gas system 30, a cooling system 40, a fuelgas system 50, a controller 60 and a temperature acquirer 70.

The air system 20 includes an air introducer 21 including a filter andan air divider.

The air introducer 21 takes in air, and the air is distributed to theoxidant gas system 30 and the cooling system 40 by the air divider.

The oxidant gas system 30 includes a filter 31, a reaction air supplier32, a reaction air supply flow path 33, a reaction air discharge flowpath 34, a first valve 35 and a second valve 36.

In the reaction air supply flow path 33, the filter 31, the reaction airsupplier 32 and the first valve 35 are disposed along the direction ofair flow.

The second valve 36 is disposed in the reaction air discharge flow path34.

The cooling system 40 includes a cooling air supply flow path 41, acooling air discharge flow path 42 and a refrigerant driver 43.

The fuel gas system 50 includes a fuel gas supplier 51, a fuel gassupply flow path 52, a fuel off-gas discharge flow path 53, acirculation flow path 54, a gas-liquid separator 55, a gas circulationpump 56, a third valve 57 (such as an injector) and a fourth valve 58(such as a purge valve).

The temperature acquirer 70 acquires the temperature of the fuel cell10. The controller 60 detects the temperature acquired by thetemperature acquirer 70.

FIG. 2 is a schematic configuration diagram of another example of theair-cooled fuel cell system of the present disclosure. Of the componentsshown in FIG. 2 , the same components as FIG. 1 are allotted with thesame numbers as FIG. 1 and will not be described here for simplicity.

In the air-cooled fuel cell system of FIG. 2 , the air system 20includes a reaction air introducer 22 configured to supply air to theoxidant gas system 30, and a cooling air introducer 23 configured tosupply air to the cooling system 40.

Each of the reaction air introducer 22 and the cooling air introducer 23includes a filter.

Each of the oxidant gas system 30 and the cooling system 40 takes in airfrom the atmosphere through the filter.

The oxidant gas system 30 includes a filter 31, a reaction air supplier32, a reaction air supply flow path 33, a reaction air discharge flowpath 34, a first valve 35, a second valve 36 and a reaction air bypassflow path 37.

In the reaction air supply flow path 33, the filter 31, the reaction airsupplier 32 and the first valve 35 are disposed along the direction ofair flow. The first valve 35 is a three-way valve and allows thereaction air to bypass the fuel cell 10 and flow from the reaction airbypass flow path 37 to the reaction air discharge flow path 34.

The second valve 36 is disposed in the reaction air discharge flow path34.

Also in FIG. 2 , a fuel gas system 50 includes a fuel gas supplier 51, afuel gas supply flow path 52, a fuel off-gas discharge flow path 53, acirculation flow path 54, a gas-liquid separator 55, a third valve 57(such as an injector), a fourth valve 58 (such as a purge valve) and anejector 59.

FIG. 3 is a flowchart of an example of the control of the air-cooledfuel cell system of the present disclosure.

The controller monitors the temperature measured by the temperatureacquirer during the operation of the fuel cell.

The controller determines whether or not the temperature measured by thetemperature acquirer exceeds the predetermined temperature threshold, orwhether or not the temperature increase rate exceeds the predeterminedtemperature increase rate threshold.

When the temperature measured by the temperature acquirer exceeds thepredetermined temperature threshold or when the temperature increaserate exceeds the predetermined temperature increase rate threshold, thecontroller decreases the opening degrees of the first, second, third andfourth valves to smaller opening degrees than the opening degreesthereof at the time of determination, or the controller stops the powergeneration of the fuel cell. The controller may close the first, second,third and fourth valves when the power generation of the fuel cell isstopped. When the temperature measured by the temperature acquirer isequal to or less than the predetermined temperature threshold or whenthe temperature increase rate is equal to or less than the predeterminedtemperature increase rate threshold, the controller may end the controlor may maintain the status quo.

When overheating occurs, the valve of the reaction air system is sealed.Accordingly, the voltage of the fuel cell is decreased by the oxygendeficiency of the fuel cell, and the power generation of the fuel cellis safely stopped. In addition, the degradation of the fuel cell issuppressed. Even when a fire occurs inside the fuel cell, the spread ofthe fire is prevented by oxygen shut-off.

Since the amount of hydrogen in moles of the sealed fuel gas system isincreased more than twice the amount of oxygen in moles of the sealedreaction air system, the oxygen inside the fuel cell system is consumed,and the voltage of the fuel cell is decreased. Since the inside of thefuel cell is sealed in a hydrogen-rich state, the progression of thedegradation of fuel cell is slowed. For complete consumption of theoxygen, the reaction air system may be sealed; the fuel gas supply maybe continued for a predetermined amount of time; and then after theoxygen is consumed to a certain extent, the fuel gas system may besealed. That is, the first and second valves are closed, and then afterthe elapse of a predetermined amount of time, the third and fourthvalves may be closed.

REFERENCE SIGNS LIST

-   10. Fuel cell-   20. Air system-   21. Air introducer-   22. Reaction air introducer-   23. Cooling air introducer-   30. Oxidant gas system-   31. Filter-   32. Reaction air supplier-   33. Reaction air supply flow path-   34. Reaction air discharge flow path-   35. First valve-   36. Second valve-   37. Reaction air bypass flow path-   40. Cooling system-   41. Cooling air supply flow path-   42. Cooling air discharge flow path-   43. Refrigerant driver-   50. Fuel gas system-   51. Fuel gas supplier-   52. Fuel gas supply flow path-   53. Fuel off-gas discharge flow path-   54. Circulation flow path-   55. Gas-liquid separator-   56. Gas circulation pump-   57. Third valve-   58. Fourth valve-   59. Ejector-   60. Controller-   70. Temperature acquirer

1. An air-cooled fuel cell system, wherein the air-cooled fuel cellsystem comprises: a fuel cell, an air introducer configured to take inair from the outside of the air-cooled fuel cell system, a reaction airsupplier configured to supply reaction air to the fuel cell, a reactionair supply flow path configured to connect the reaction air supplier anda reaction air inlet of the fuel cell, a reaction air discharge flowpath configured to connect a reaction air outlet of the fuel cell andthe outside, a cooling air supply flow path configured to connect theair introducer and a cooling air inlet of the fuel cell, a fuel gassupplier configured to supply fuel gas to the fuel cell, a fuel gassupply flow path configured to connect the fuel gas supplier and a fuelgas inlet of the fuel cell, a fuel off-gas discharge flow pathconfigured to connect a fuel gas outlet of the fuel cell and theoutside, a temperature acquirer configured to measure a temperature ofthe fuel cell, and a controller; wherein the reaction air supply flowpath comprises a first valve in a region downstream of the reaction airsupplier and upstream of the reaction air inlet of the fuel cell;wherein the reaction air discharge flow path comprises a second valvedownstream of the reaction air outlet of the fuel cell; wherein the fuelgas supply flow path comprises a third valve upstream of the fuel gasinlet of the fuel cell; wherein the fuel off-gas discharge flow pathcomprises a fourth valve downstream of the fuel gas outlet of the fuelcell; wherein the fuel cell has a structure that a reaction air manifoldand a cooling air manifold are independent of each other; wherein thecontroller monitors the temperature measured by the temperatureacquirer; and wherein, when the temperature measured by the temperatureacquirer exceeds a predetermined temperature threshold or when atemperature increase rate exceeds a predetermined temperature increaserate threshold, the controller decreases opening degrees of the first,second, third and fourth valves.
 2. The air-cooled fuel cell systemaccording to claim 1, wherein the air-cooled fuel cell system furthercomprises a cooling air discharge flow path configured to connect acooling air outlet of the fuel cell and the outside, and wherein thecooling air discharge flow path comprises an air pump or air fan.
 3. Theair-cooled fuel cell system according to claim 1, wherein the controllercloses the first, second, third and fourth valves when power generationof the fuel cell is stopped.